This invention relates to a method for inspecting the quality of a gas sensor having a sensing element. The present invention also relates to a manufacturing method utilizing the inspecting method of the present invention. Furthermore, the present invention relates to an inspecting apparatus preferably used for performing the inspecting method of the present invention.
Conventionally, the quality inspection for a gas sensor having a sensing element generally includes visual check of the presence of any surficial crack on the sensing element, measurement of gas sensor output characteristics, and check of sensing element airtightness.
However, according to the above-described conventional gas sensor inspection method, it was difficult to find out hidden cracks in a gas sensing element. The hidden cracks include micro cracks or non-through cracks. The gas sensor, if its sensing element has hidden cracks not detectable through the visual inspection, will be judged as non-defective products and will be put into circulation in the market and installed in a practical engine or other device.
The size of such a hidden crack generally increases or grows when the gas sensor is subjected to high-temperature or severe environment during the use of gas sensor. This will possibly lead to the deterioration of gas sensor output characteristics or cause other problems. In other words, the presence of a hidden crack will invite deterioration in the durability of gas sensor.
In view of the above problems, the present invention has an object to provide a method of inspecting the presence of a hidden crack in a gas sensing element to prevent a defective gas sensor having such an invisible crack in the sensing element from being put into circulation in the market.
Another object of the present invention is to provide a manufacturing method relating to the inspecting method of the present invention.
Furthermore, another object of the present invention is to provide an inspecting apparatus relating to the inspecting method of the present invention.
To accomplish the above and other related objects, the present invention provides a first method for inspecting the quality of a gas sensor having a sensing element characterized in that an impact force is applied to the sensing element to enlarge the size of a hidden crack to a visible level, thereby revealing the presence of the hidden crack.
According to the first inspecting method of the present invention, it becomes possible to change a hidden crack, if involved in the gas sensing element, into a visible and easily detectable crack by applying an impact force. Namely, when the gas sensing element involves a hidden crack, it is generally difficult to find out the hidden crack. However, the first inspecting method of the present invention makes it easy to find out such an invisible crack by forcibly increasing the crack size to a visible level.
Accordingly, if the gas sensing element involves a hidden crack, the first inspecting method of the present invention makes it possible to easily detect such at a defective gas sensing element.
Therefore, the first inspecting method of the present invention prevents a defective gas sensor having an invisible crack in the sensing element from being put into circulation in the market.
As described above, according to the first inspecting method of the present invention, it becomes possible to provide a gas sensor inspecting method capable of preventing a defective gas sensor having an invisible crack in the sensing element from being put into circulation in the market.
The present invention provides a second method for inspecting the quality of a gas sensor having a sensing element disposed in a tubular housing, comprising a step of placing the housing of the gas sensor in a holder which is fixed to a distal end of a shaft, the shaft being swingable on a vertical plane about a proximal end thereof serving as a pivot, and a step of applying an impact force to the sensing element by releasing the holder holding the gas sensor from a predetermined higher position so as to swing downward about the pivot of the shaft due to gravity and then hit a striking plate disposed on a swing path of the holder, thereby applying an impact force to the sensing element. According to the second gas sensor inspecting method of the present invention, the step of applying the impact force to the sensing element is performed plural times from different directions including at least two directions substantially perpendicular to each other with respect to said gas sensor, thereby enlarging the size of a hidden crack to a visible level and revealing the presence of the hidden crack.
According to the second gas sensor inspecting method of the present invention, it becomes possible to provide a gas sensor inspecting method capable of surely preventing a defective gas sensor having an invisible crack in the sensing element from being put into circulation in the market.
The present invention provides a method for manufacturing a gas sensor comprising a step of inserting and fixing a sensing element in a tubular housing and a step of applying an impact force to the sensing element disposed in the housing, thereby confirming that the sensing element includes no visible crack.
According to the manufacturing method of the present invention, it becomes possible to change a hidden crack, if involved in the gas sensing element, into a visible and easily detectable crack by applying an impact force. Namely, when the gas sensing element involves a hidden crack, it is generally difficult to find out the hidden crack. However, the manufacturing method of the present invention makes it easy to find out such an invisible crack by forcibly increasing the crack size to a visible level.
Accordingly, when the gas sensing element involves no visible crack even after the impact force is applied to the gas sensing element, it can be confirmed that the sensing element includes no hidden crack.
According to the manufacturing method of the present invention, it becomes possible to provide a gas sensor manufacturing method capable of obtaining a gas sensor having no invisible crack in the sensing element.
Furthermore, the present invention provides an apparatus for inspecting the quality of a gas sensor. The inspection apparatus of the present invention comprises a holder for holding a sensing element of a gas sensor, a shaft having a proximal end serving as a pivot and a distal end to which the holder is fixed, the shaft being swingable about the pivot so that the sensing element held in the holder can be released from a predetermined higher position, and a striking plate disposed on a swing path of the holder so that an impact force is applied to the sensing element when the sensing element held in the holder is released from the higher position and collides with the striking plate.
According to the inspecting apparatus of the present invention, it becomes possible to simply and accurately perform the quality inspection of a gas sensor.